Viral infection of mammalian cells causes rapid and profound changes in the expression patterns of specific cellular genes. The proteins encoded by these genes, the viral stress-inducible genes (VSIG), are responsible for maintaining viral homeostasis in the infected cells. Many of the VSIG can also be induced in uninfected cells by interferons (IFN) or double-stranded (ds) RNA, common byproducts of viral infection. Here, we propose to identify the patterns of changes in cellular gene expression profiles in response to type I IFN, dsRNA and Sendai virus infection. Customized cDNA microarrays will be used to measure the levels of relevant cellular mRNAs in virus-infected or IFN/dsRNA treated cells and compared with the corresponding levels in untreated cells. Mutant cell lines, specifically defective in IFN or dsRNA-elicited signaling pathways, will be used to assess the contributions of these pathways in gene induction by Sendai virus. Furthermore, we propose to delineate the distinct signaling pathways used by the three agents to induce transcription of a common subset of VSIG that encode the P56 family of proteins. For this purpose, we will use mutant cell lines deficient in specific components of the Jak-STAT, the IRF3 and the NFkappaB signaling pathways as well as chemical inhibitors and siRNAs. DsRNA signaling uses Toll-like receptor 3 for inducing transcription of the P56 family of genes and it has recently been shown by us that receptor tyrosine phosphorylation is essential for this process. We propose to identify the roles of specific phosphotyrosine residues of TLR3 in mediating dsRNA-signaling that leads to the induction of P56 and other genes. The biochemical basis of the need for TLR3 phosphorylation will be investigated by examining activation of the relevant transcription factors and protein kinases in cells expressing Wt or mutant TLR3 proteins. These studies will illuminate the modes of cross-talk between the TLR and the Jak-STAT signaling pathways for appropriate gene induction in virus-infected cells.